The present invention relates to an iron casting process and an iron foundry molding apparatus by which a cast-iron element having a non-iron interior area may be produced by utilizing a molding core. The invention further relates to an iron casting having a non-iron interior area. More particularly, the present invention relates to an elongate cast-iron element such as a camshaft, crankshaft or the like for internal combustion engines and to methods and apparatus for producing same.
In the casting of an elongated cast-iron component formed as a hollow body defining an elongated interior cavity, such as for example an internal combustion engine camshaft, or crankshaft, a suitable elongate core is set in the forming mold into which the molten iron is poured, thereby to form the interior cavity. Conventionally, sand cores are often utilized for this purpose, but with the disadvantage that sand cores produce a relatively rough interior surface of the casting that accordingly must be machined. Moreover, depending on the diameter and length of the core, it is often necessary to support the core at one or more locations along its length. Finally, in actual practice, sand cores have been found to fail entirely beyond a given length to diameter ratio, such as for example 500 millimeters in length and 10 millimeters in diameter.
An alternative to the use of sand cores is disclosed in British Patent No. 11 91 202 which discloses the use of a molding core assembly consisting of steel tube containing a steel bar coated with insulating material. According to this process, the steel bar is drawn out of the steel tube after molten iron has been formed in the mold about the tube whereupon it becomes a part of the casting. A fundamental drawback of this method, however, is that a quench zone forms at the interface between the steel tube and the cast iron which is very hard and difficult to bore. Furthermore, steel tubes of the type utilized in this process are relatively expensive.
An elongated casting with a relatively smoothly surfaced longitudinal interior throughhole may be produced utilizing a graphite rod as the molding core, as disclosed in British Patent Specification 15 96 442. Disadvantageously, however, such graphite rods are relatively crack-sensitive and furthermore have a very porous surface in which moisture, grease and like residue may accumulate as a result of ordinary skin contact, which for example may lead to casting defects such as blow holes. As a result, graphite rods require special handling measures which in actual practice may be infeasible. Moreover, as with sand cores, an elongate graphite core requires the use of braces along the central zone of its length when the length to diameter ratio of the core exceeds a given value.